1. Field of the Invention
The present invention relates to an automated drive train for a motor vehicle comprising a single friction clutch, which is actuated by an actuator and is connected at the input side to the motor of the vehicle, and a step transmission connected to the output side of the clutch. The transmission comprises a first plurality of wheel sets for engaging and disengaging corresponding forward gears and a corresponding plurality of positive gear shift clutches, each having synchronization means. The gear shift clutches can be actuated for engaging and disengaging the gears by a second plurality of second actuators. A controller coordinates the control of the first actuator with the second actuators.
The invention further relates to a method for controlling a drive train of a motor vehicle, which comprises a first plurality of wheel sets for engaging and disengaging the corresponding forward gears and a corresponding plurality of positive gear shift clutches, each having synchronization means. The gear shift clutches can be actuated for engaging and disengaging the gears by a second plurality of second actuators. When changing gears, the first actuator is controlled to be coordinated to the second actuators.
2. Description of Related Art
Such an automated drive train and such a method are disclosed in WO93/10378. In transmissions for motor vehicles, particularly passenger vehicles, one distinguishes generally between automatic transmissions and manual transmissions. The former comprise a hydro-dynamic torque converter and a plurality of planet wheel sets, which are controlled by overlapping braking and coupling means, so that no interruption of the driving force occurs when changing gears.
Manual transmissions in contrast are step transmissions with a layshaft arrangement. When changing gears, an interruption of the traction force occurs between the time one gear is disengaged and a new gear is engaged, because the friction clutch associated with the transmission is opened (typically a starting clutch configured to be a dry clutch). Thereby, the motor is completely decoupled from the transmission and therefore also from the vehicle drive wheels.
It is standard in automotive transmissions of today that a locking synchronizer is provided for each positive gear shift clutch for engaging and disengaging gears. A locking synchronizer comprises a synchronizing means (typically a friction coupling) through which a matching of the rotary speed between a wheel set and a shaft (drive shaft) takes place when the friction clutch is open, i.e. not under load. A locking means of the synchronizer prevents or impairs a positive engagement of the gear shift clutch (i.e. the engagement of the gear) until a matched speed is nearly attained.
While the traction force decrease when changing gears by manual shifting is considered to be not particularly unpleasant, the associated xe2x80x9cnickingxe2x80x9d of the automobile is considered to be less comfortable when the step transmission is automated. In automated step transmissions, the actuation of the friction clutch and gear shift clutches is undertaken by a controller which coordinates actuators, instead of being done by the hand and foot. The traction force interruption is found to be uncomfortable, because with an automated step transmission, the driver is not occupied during gear changing.
Various attempts have been made to mitigate this problem. In the step transmission known from WO93/10378, an attempt is made to shorten the duration of the traction force decrease interruption. This is achieved by two measures. In the transmission disclosed there, two gears, not in sequence with one another, are arranged in one shifting group. In addition, the locking synchronizers of more than one group are activated simultaneously when changing gears. In other words, when disengaging the previous gear (old gear), the synchronization to the rotary speed of the following gear takes place not only with the associated locking synchronizer, but in addition with the locking synchronizer of an additional gear. The times associated with shifting are to be reduced, which achieves shorter shifting times. The duration of traction force decrease is therefore reduced.
A further principle to reduce the traction force decrease is disclosed in the German patent application DE 44 01 812. Instead of a single friction clutch at the input side, a double clutch system is provided. One clutch of the double clutch system associated with the transmission input shaft is for the gear ratios one to five, while the second clutch is associated with the highest gear, namely the sixth gear. During shifting in the lower gears, where the first clutch is first completely opened in known manner and then closed after the shifting, the second clutch, normally open, is closed for a short period, so that the torque of the sixth gear is supplied to the drive shaft of the transmission for a short time. However, when shifting in the lower gears, a considerable traction force decrease still occurs because the torque of the sixth gear is considerably less than that of the lower gears.
The German patent application DE 29 24 656 discloses a further shift transmission in which a single friction disconnection clutch is provided at the input side and in which the wheel set for the second gear does not have the conventional gear shift clutch, but has a wet multi-disc friction clutch. Furthermore, the idler of the first gear is mounted freely on the corresponding shaft. Thus when changing from the first to the second gear, the torque of the motor at the input side of the transmission can be applied to the second gear without opening the friction disconnection clutch and without decrease of the traction force. The change in higher gears however takes place with traction force decrease since for these changes the input side disconnection clutch must be opened.
An automated change speed transmission is disclosed in the German patent application DE 197 35 759. The gear shift clutches for engaging and disengaging the gears are configured as pure positive clutches in the form of claw or draw key couplings. Shifting takes place in that the relative angular position of the elements to be connected is monitored and a signal is output in the ready condition. One gear shift clutch is then opened by a highly dynamic hydraulic system and a new gear shift clutch is closed. When actuating the gear shift clutches, an input side friction disconnection clutch is held in slip condition.
In addition, an automated step transmission with traction force support is disclosed in the German patent DE 195 48 622.
Finally, the so-called xe2x80x9cgenuinexe2x80x9d double clutch transmissions are known, for example from the German patent DE 38 12 327. Two parallel friction clutches are provided on the input side of the transmission. The two clutches are associated with two parallel branches of the transmission, where the parallel interconnection is achieved with a hollow shaft construction. The gears are alternately located on one and then the other drive branch, so that in overlapping operation, the motor torque at the input side can transfer from one branch to the other branch without any traction force decrease.
The mentioned WO93/10378 suffers from the drawback that the central clutch is opened when changing gears so that an uncomfortable decrease in the traction force takes place when shifting, although the interruption time can be optimized. In the transmission of DE 44 01 812, the construction is comparatively complicated due to the double clutch arrangement at the input side. Further, the traction force support can only maximally transmit the torque of the sixth gear to the drive wheels. The complexity of DE 29 24 656 is also considerable, in particular due to the free wheel for the first gear. The concept of DE 197 35 759 cannot completely avoid traction force interruption and requires a very stable construction. The true double clutch transmission, as disclosed in DE 38 123 27 requires not only constructive complexity due to the two clutches, a comparatively long hollow shaft construction is necessary which makes the transmission expensive.
In view of the above, the object of the present invention is to provide an automated drive train and a method of controlling a drive train for a motor vehicle of the mentioned type, in which gear changing is as fast as possible and in which the greatest possible traction force support can be achieved, where only one friction clutch is present, provided as a disconnection clutch.
The object is achieved with the mentioned automated drive train, by providing synchronization means suitable for synchronizing under partial load and a controller for controlling actuators such that at least one type of gear change takes place without the clutch being completely open. In the mentioned method for controlling the drive train, the synchronization means are suited for synchronizing under partial load and the actuators are controlled such that the friction clutch is not completely opened for at least one type of gear change.
According to a further aspect of the invention in the mentioned method, the same drive train is operated in one of three possible modes to carry out the gear change, depending on the conditions of the gear change to be made, wherein the three possible modes include gear changing with an opened friction clutch, a closed friction clutch or a slipping friction clutch.
The object is completely achieved in this manner.
By departing from the idea that the input side clutch configured as a separating clutch must always be open in a step transmission during the gear change, the clutch is not completely opened in the first aspect of the present invention, but remains either completely closed (mode B) or is operated in slip condition (mode A). The drive connection between the motor of the vehicle and the transmission is not released at any time during the gear change.
With suitable configuration of the gear shift clutches, shifting can take place such that when the gear to be disengaged is initially still engaged the torque is completely transferred to the gear shift clutch of the gear to become engaged. This results in a condition of substantially no load for a short time on the gear shift clutch of the gear to be disengaged, so that this gear is easily disengaged in this short time interval. In the following synchronizing phase of the gear changer for the gear to be engaged, the input side friction clutch remains at least partially closed, so that the torque from the motor is transferred via the friction clutch working in slip operation and via the synchronization means for the gear to be engaged to the drive wheels of the vehicle.
With this feature, that the synchronization means are suited for synchronizing under partial load, it is possible to configure the step transmission of the present drive train without further synchronization means apart from the respective gear shift clutches. This has the advantage that gear shifting under partial load can be carried out both when shifting upwardly and shifting downwardly. In contrast, a central wheel set brake would otherwise be necessary for shifting upwardly and for shifting downwardly an additional drive means would be necessary.
The automated drive train and the corresponding method provide gear shifting according to a first aspect of the invention with traction force support, in contrast to WO93/10378. In contrast to DE 197 35 759, the gear shifting takes place without traction force interruption at any time. Further, it is not necessary to provide two friction clutches at the input side and a hollow shaft construction is not required. Finally, the gear shift clutches of the drive train are configured to make a positive engagement, so that the entire actuator mechanism with an engaged gear is relieved and no additional energy is required. This is also an important advantage for reasons of reliability and efficiency.
According to the further aspect of the invention, the same gear change of a drive train can be carried out in one of three different modes depending on the respective conditions. Thus, depending on the respective conditions, more comfortable or more sporty shifting can be carried out.
Preferably, at least one of the second actuators is configured to control two gear shift clutches. This feature reduces the complexity of the actuator system as a whole for automating the drive train. Preferably, the two gear shift clutches are associated with gears which are not in sequence with one another. In other words, it is achieved that neighboring gears are actuated by different actuators and therefore can be engaged and disengaged independently from one another. The greatest possible flexibility in the control of the actuators of the transmission is achieved.
Particularly preferred is when the further two gears lie between two gears to be shifted. This feature has the advantage that two gears are always operated by one actuator, which in practice are never shifted in sequence. Since the present arrangement does not concern a sequential transmission, the sequence of the gears when shifting is not limited to neighboring gears. Thus it is generally possible not only in manual transmissions but also in automated drive trains to carry out shifting directly from one gear to the gear following the next gear, for example to shift from the fourth gear to the sixth gear.
With the feature that two further gears lie between the two gears being operated by one actuator, shifting without traction force interruption is possible not only from one gear to the next gear, but also the gear after next gear. Only shiftings using two gear shift clutches, which are operated by one actuator, cannot be performed with this shifting strategy, so that a traction force interruption occurs. However, it has been shown that precisely those shiftings to a gear second following the next gear are practically never used by a driver.
The shift transmission preferably comprises six forward gears and three second actuators when further all three second actuators are configured to control two gear shift clutches each and when finally each of the two gear shift clutches is associated with two gears which are not neighboring one another. With this feature it is possible to carry out all gear shiftings of a six gear transmission from one gear to the respective next gear while providing traction force support.
It is particularly preferred when precisely two further gears lie between all of the non-neighboring gear pairs. This is of advantage for the mentioned reasons, because a driver in practice will never require a shifting from one gear to the gear second following the next gear. All other shiftings can be carried out with traction force support. For a transmission with exactly six gears, this rule results in that the non-neighboring gear pairs are the gears 1 and 4, the gears 2 and 5 and the gears 3 and 6.
The synchronization means preferably provide a cone synchronization. Cone synchronizers are proven synchronizing elements and it is comparatively easy to configure such elements for the drive train of the present invention. The cone synchronizers preferably comprise a multiple cone. With a multiple cone, the shifting force of the synchronization means can be reduced on the whole. The synchronizing process can be accelerated.
In a further preferred embodiment, the cone synchronizers comprise a cone angle of more than 6xc2x0. The synchronization means can be better controlled and self-locking can be avoided.
In a further preferred embodiment, the synchronization means comprise multi-disc synchronizers. Multi-disc synchronizers are easily controllable and are better adjustable.
In a preferred embodiment, the gear shift clutch comprises an asymmetric tip of the gear teeth on a sliding sleeve actuated by the actuator. The sliding sleeve and the coupling body are better passed through each other under load. Further preferred is when the gear shift clutch comprises a tooth profile without back cutting on the sliding sleeve actuated by the actuator or on the coupling body. In this manner, the gear being actuated by this gear shift clutch is easier to disengage.
In a further preferred embodiment, the gear shift clutch comprises a tooth profile with back cutting on its coupling body or on the sliding sleeve. This feature does not impair the disengagement of the gear under load.
It is of advantage to provide a central lubrication for the wheel sets and the associated gear shift clutches. No losses due to splashing of the gear set occur as does with an immersion lubrication. The shift elements are better and more reliably supplied with oil. Further, the central lubrication ensures that the heat arising by synchronization under load is better dissipated.
In the method of the present invention, it is preferred during a gear change in modus A, B when a synchronizer of the gear to be engaged is operated in slip condition before disengaging the presently engaged gear, to take up the torque present at the input side of the transmission. With this feature, the gear shift clutch of the engaged gear is free of load for a time interval, so that this gear can also be disengaged under load.
Of advantage before disengaging the engaged gear is to provide a further synchronizer in addition to the synchronizer of the gear to be engaged. The further synchronizer is that of a gear not involved in the gear change. The further synchronizer is operated in slip condition to partially take up the torque present at the input, for engaging the gear to be engaged.
In a particularly preferred embodiment, the gear shift clutch associated with the engaged gear is biased in the disengaging direction before its disengagement. With the biasing, the gear to be disengaged xe2x80x9cjumpsxe2x80x9d out as soon as the load free condition is reached.
In a further preferred embodiment, the friction clutch is partially opened during the shifting (mode A) and/or the torque provided by the motor is reduced by means of a motor actuator (modes A, B). The torque present at the input side of the transmission is reduced to prevent overloading of the synchronizer of the gear to be engaged. The motor actuator can normally interact in the motor management to reduce the input torque by xe2x80x9celectronic gas reductionxe2x80x9d.
Finally it is preferred in modes A, B that the torque input to the shift transmission, after having disengaged the previously engaged gear, is reduced for a short time, after reaching the synchronization speed and during the engagement of the gear to be engaged. This reduces or completely avoids differences in rotary speeds when transferring the torque from the synchronizer to the idler of the associated wheel set.
Further advantages and features will become apparent from the following description of preferred embodiments. It will be understood that the above-mentioned features and those to be discussed below are not only applicable in the given combinations, but may also be present in other combinations or taken alone without departing from the scope of the present invention.